I found that with java ferns, it takes a while for them to attach and get settled in. Then it's like you turned on a switch, they just start growing a ton. When I had a bunch of plantlets, I put them in a critter keeper and set it in a window that gets a good amount of light. I would do a daily 75%-50% water change and they would take off. Then I'd move them into the larger tank when they were ready.
Hope this helps,
Scouter
Hope this helps,
Scouter